Does UV Work in Swimming Pools?

The short answer is yes. But don’t stop there.

There is an almost hysterical run toward using UV (ultra violet) light to “better” treat and disinfect swimming pools against bather and environmental waste. And you can’t stop at the answer above. You have to understand what UV treatment is actually doing. Like everything, there are pros and cons. There are also myths that must be dispelled and put to rest.

First the facts. There are 3 types of UV. UV-A: causes wrinkles in our skin and “burning”. UV-B aids in the production of Vitamin D. Both of these are able to penetrate the earth’s atmosphere. UV-C is used commercially and personally to disinfect food and objects. UV-C cannot penetrate the atmosphere and must be artificially created.

UV-C is excellent in sanitizing against bacteria, viruses, cysts & certain protozoa (including cryptosporidia and giardia – usually introduced from bather or environmental fecal matter – of which both are chlorine and halogen resistant). It does not allow algae to grow and multiply. It is non-irritating to mucous membranes, eyes and ears. It does not affect your pool’s water balance. It aids in reducing (not eliminating) chloramines and chlorine demand.

How does UV-C actually work? UV-C works works by disrupting the bacteria cells DNA and RNA. When the DNA and RNA are disrupted, the bacteria and viruses can not reproduce and multiply. Please note: UV-C DOES NOT KILL ANYTHING!

That’s the first myth or bit of information debunked. UV-C does not kill anything. Furthermore UV-C will NOT remove any micro-organisms. The other things that UV-C will not do are:

  • Protect against re-contamination. As swimmers enter the water with “new” bacteria and micro-organisms, those must be treated.
  • Work well in cloudy water. Cloudy water will effectively block the absorption of UV-C to do its job.
  • Work well in the presence of heavy metals (dissolved iron, copper and manganese). Iron effectively blocks UV-C absorption.
  • Work well in areas of high Calcium Hardness (over about 300 ppm). Areas of hard water will tend to be scale forming. Scale WILL form on UV-C tubing preventing its effectiveness.
  • Work as a stand alone sanitizing system. UV-C is meant to work as a supplement with chlorine, salt, bromine. Ionizers (Nature2, Frog, etc), biguanides (Soft Swim, Baquacil, etc) are not compatible.
  • Oxidize anything. Shock treatments (using either chlorine or non-chlorine shock products) must be done regularly to oxidize contaminants and certain other unfiltered matter.

Keep in mind that the way that UV systems are constructed, they must be properly maintained all of the time in order to be effective. I mentioned above that UV is rendered ineffective when the pool water is cloudy. The UV light cannot penetrate the turbidity of the water. The water must be clear. The same holds true of the UV generator.

The bulb of the UV generator is typically surrounded and protected by a quartz tube. The problem is that the quart tube will get cloudy; and it will get cloudy quickly. How quick? The “occlusion rate” (how cloudy it gets) is, on average, about 5% per week. What does that mean to you? It means that after about 7 to 8 weeks, almost 50% occlusion will have occurred. Or in other words, only about 50% of the UV light is able to work.

In areas of high calcium hardness or high scaling or hard water or high metals (iron, copper, etc), the UV generator tubing will scale and cloud even faster. Proper, weekly chemical cleaning of the tube is essential to remove and eliminate scale and naturally occurring bio-film build up. Using a bio-film remover such as AquaFinesse Pool Water Care tablets will aid in the cleaning. Otherwise, clean with a mild acid cleaner.

Is a UV-C system right for you? You will have to answer that question. The price range for a good UV system for the average swimming pool is anywhere from about $1300.00 to $2500.00. That’s a lot of money and can purchase of lot traditional good, hard working chemicals and products.

Do your research. Anyone claiming bacteria kill is completely misrepresenting the product. Remember, if it sounds too good, it probably is.